Modern magic lanterns; a guide to the ... - Yesterday Image

—CHAPTER X.^be ©pticalSi^stem.We have considered the light and the mechanical portionsof a lantern, and have intentionally reserved the mostimportant part of all i.e., the lenses by which the image ofthe slide is thrown upon the screen, until last. The opticalsystem consists of the condenser, the function of which isnot to condense the light upon the slide, but to divert the raysfrom the lamp so that the margins of the slide as well asthe centre shall be illuminated by rays which can reachthe objective, and the latter itself which is used to secure asharp and brilliant picture.That the purpose of the condenser is really what wehave said can be seen on reference to Fig. 49, in which areFig. 49.Diagram showing the Lantern, but without Condensers.sketched the arrangements of a lantern and screen minusthe condenser. It is evident, since light under ordinaryconditions travels in straight lines, that the only direct hghtwhich can fall on the screen d from the light a, will be that